The present invention relates to an image forming apparatus that carries out image formation after adding a cutting mark indicating the cutting position to the image data using which the image formation is to be done.
In recent years, in image forming apparatuses, in some cases images are formed on sheets by attaching cutting marks indicating the position of cutting to the image data using which image formation is to be done. Because of this, it is possible to increase the efficiency of work since the work of cutting the sheets using a cutting machine becomes easy after the image formation has been completed.
Normally, cutting marks are made on all pages, that is, cutting marks are made on both sides of the sheet when forming images on both sides of the sheet (see, for example, Patent Document 1). In Patent Document 1, a document preparing apparatus has been disclosed that prints on single sheets of paper such as visiting cards, postcards, etc. In concrete terms, this is a technology in which one side of the sheet is taken as it is as the reference side during printing and the number of cutting operations is reduced. In the document preparing apparatus disclosed in Patent Document 1, the cutting marks are printed automatically on the pages on both sides of the sheet.
Therefore, when cutting marks are printed on both sides of the sheet, the positional relationship between the cutting marks that determine the cutting position is not matched but is shifted between the front and back surfaces of the sheet, if the cutting is done matching with the cutting mark printed on one surface of the sheet, then it is possible that the cutting mark printed on the other side of the sheet remains uncut. An unnecessary cutting mark which is an image other than the image data remaining on the sheet causes the problem of reduction in the image quality.
Further, in Patent Document 2, in the printing field, particularly in the imposition method of carrying out imposition operation of multiple layers of design images in order to prepare printing masters and in a voucher design system using such a method, an imposition method has been disclosed that has a setting process of setting the parameters of positioning marks. In terms of the concrete technical details, it has been disclosed that the type is set in the register mark setting screen indicating on which of the front and back surfaces is the register mark to be placed. In this technology, it is necessary for the user to select whether or not to place register marks and then make the specification, and hence the procedure is complicated. In addition, it is up to the user to determine on which of the front and back sides is the register mark to be placed, hence the register mark is placed on an arbitrary surface, and even the purpose of asking the user whether or not to place the register mark is merely for the sake of convenience of the user, and no concrete purpose has been considered.
Patent Document 1: Japanese Unexamined Patent Application Open to Public Inspection No. 9-109505
Patent Document 2: Japanese Unexamined Patent Application Open to Public Inspection No. 8-241399
However, in image forming apparatuses that form images using the electro-photographic method, investigations by the inventors revealed that a special problem occurs when cutting marks are placed on both sides of the recording sheet. That is, in the electro-photographic method, the image forming processes include a heating and pressure applying fixing process that fixes the toner image on the recording sheet by applying heat and pressure. Because the water content in the sheet evaporates due to being heated and also the fiber structure constituting the sheet becomes soft when the sheet is heated during this heating and pressing process, there is the phenomenon that the sheet shrinks after the heating and pressing fixing process. When forming images on both sides of the sheet, even when images of the prescribed size are formed on the front surface, because of the shrinking phenomenon of the sheet, the sheet and the formed image will have a slightly reduced size. Next, during the formation of images on the back surface, when image forming is done under the same conditions on the second surface of the sheet having a reduced size image formed on a reduced size first surface, the size of the images on the first surface will be slightly smaller than the size of the images on the second surface. As a consequence, there will be a shift in the positions of the images on the first and on the second surfaces. When the images formed are cutting marks, basically there will be a shift in the position because of shrinking of the sheet during the fixing process, even if-image formation is done at the same position in the front and back surfaces. When the cutting operation is made taking as reference the cutting marks on either the front surface or on the back surface, it is possible that the cutting mark that was not taken as the reference remains on the sheet after cutting, and hence the image quality goes down.
Furthermore, in the case when the problem described above could be solved, when a plurality of sheets on which image forming has been completed are stacked on the sheet discharge tray in the image forming apparatus, the user has to take the bundle of sheets by hand up to the cutting machine. At this time, if the surface on which no cutting marks have been formed is the upper surface facing upward of the bundle of sheets, the user has to turn that bundle of sheets upside down, and if the bundle of sheets contains several hundred sheets, it becomes difficult to turn upside down the bundle of sheets easily, and hence the handing of the bundle of sheets becomes-complicated.